Field of the Invention
This invention relates to a detector for use in an image scan-and-read-out system, and particularly to means for detecting pieces of information other than images when used in an image read-out system using a flat type light-transmission optical unit for reading an image which is swept with a scan beam of light.
There has been proposed a flat type light-transmission optical member for use in collecting the light reflected from or passing through an image-bearing sheet being swept with a scan laser beam thereby to direct the so-collected light to a photomultiplier or some other kind of photo-electric converter (See Light-transmission sheet material disclosed in Japanese Unexamined Patent Publication No. 55(1980)-88005). The flat type light-transmission optical member is herein below referred to as a "light-transmission member". In case such light transmission member is used in collecting the light reflected from or passing through a photographic film, a photogravure or some other kind of sheet material bearing pieces of information in the form of images or pictures being swept with a scan beam of light, it is necessary to detect the presence (or absence) of the sheet, any scratches on the sheet, the intensity of the scan light and other required information. Specifically, a start signal indicating the start of image scanning is generated in response to the arrival of the image bearing sheet at the scanning station, the light from or passing through a selected portion of the sheet is detected for use as a reference with respect to which a determination is made as to whether any modification in the amount of the light reflected or passing through the sheet other than the portion selected for reference is caused by an image or by a scratch on the sheet, and the intensity of the scan beam is detected to control the amplification factor of the photo-electric converter.
The output signal from the photo-electric converter can be used for certain detections as required. Indeed, the output signal from the photo-electric converter can be used to detect the arrival of the sheet at the scanning station and to determine the intensity of the scan beam. But, this is impossible or useless in detecting a scratch on the sheet because of the incapability of distinguishing the reflected or passing light from the scan light. There is known an image read-out system in which a stimulable phosphor sheet storing an X-ray or radiation image is exposed to an exciting light to cause a luminous image to appear in the sheet, and then the luminescence is collected with the aid of a light-transmission read-out (See U.S. Pat. Ser. Nos. 105,240 and 168,805). In such an image read-out system the luminescence from the luminous image is at a relatively low intensity and an optical filter is put ahead of the photomultiplier to select the luminescence as required eliminating the component of exciting light which, otherwise would eventually appear as a noise component. In this case the output signal from the photomultiplier contains no exciting light component, and therefore the intensity of the exciting light cannot be detected from the output signal from the photomultiplier. When the output signal happens to decrease, a determination cannot be made as to whether the instantaneous decrease is due to a scratch or a dark portion of the image not a defect on the sheet. In order to make a detection as required, it is necessary to provide extra light-collecting means such as an optical fiber, glass rod or acrylic rod at a place where it can receive the light reflected from the sheet, and to provide an associated photo-sensor to which the light-collecting means directs the so-collected light. This requires the provision of extra components exclusively for the purpose, and hence a corresponding increase is caused in the manufacturing cost. Also, in this kind of light collection the "shading effect" must be reduced to the minimum possible. Specifically, the output signal from the light collecting means is required to show a relatively small variation over the scan range across the sheet, and in order to meet this requirement these must be provided an increased number of optical elements, for instance, photo-sensors allotted for the purpose, and accordingly an increase in cost results.